Added ability to configure a node's width and height separately

[terahn]

From #336, added the ability to configure a node's width and height separately when using custom nodes. For example:

node:  {
    size: {
        width: 300,
        height: 200,
    },
}

This does not break any existing configurations. Using this with the standard node shapes will cause the links to disappear, however there is no reason to use a different height and width for these anyways since the d3 shapes cannot be stretched. I explicitly stated that this should only be used for custom nodes in the documentation, as well as added a console.warn() to discourage this incorrect use.

I think this is an important feature for people who want to use custom nodes because when using a custom node with an unequal height and width, unnecessary white space has to be added in order for the node to not be cut off. For example:

Let me know your thoughts on this!

[danielcaldas]

Thanks! This is looking great, just have a few comments that I would like you to address before we move on and merge this. 👏 👏

[terahn]

Thanks for the feedback, I've implemented those changes now in the latest commit.

p.s. Ignore the flurry of force pushes, I messed up a bit initially and wanted to clean up the commits a bit 😆

[danielcaldas]

Ready to go 🚀